The International Telecommunication Union-Telecommunication (ITU-T) has developed a recommended standard for Packet-Based Multimedia Communications Systems. The standard is called H.323. The recommendation envisions that there can be one or more zones in a given H.323 communications system. A zone can contain H.323 functional entities such as terminals, gateways, multipoint control units (MCUs), communications networks, and their resources including bandwidth, ports, buffers, and others.
H.323 mandates that a functional entity, which is called a gatekeeper, manages the resources within a given zone. A gatekeeper is an intelligent functional entity used to transfer signaling messages into and out of zones and domains, and contains the intelligence necessary to establish communication between communicating entities. Typically, the gatekeeper manages a single zone.
H.323 systems, however, are not limited to single zones. In fact, a large H.323 system can consist of multiple zones with a boundary between the zones. The zone boundary can be physical or logical.
While the H.323 standard defines certain requirements, the standard does have some gaps. For example, typically, certain H.323 signaling messages are transmitted between H.323 entities and the gatekeeper in a given zone only. These signaling messages include location, zone admission, bandwidth, discovery, registration, and/or other signaling messages. These messages, however, may have to travel between multiple gatekeepers in their respective source-destination paths because the first receiving gatekeeper may not be able to process the signaling message. If the first gatekeeper cannot process the signaling message, it is sent for processing to another zone's gatekeeper. The H.323 standards do not specify how these signaling messages can be sent between the gatekeepers in a multiple-gatekeeper environment.
Further gaps exist in H.323 requirements. For example, H.323 does not specify the possible logical architectural relationships between the gatekeepers for communications. If the gatekeepers are arranged in a hierarchical relationship, a hierarchical gatekeeper architecture may not even maintain a zone. Rather, the gatekeeper may manage a number of gatekeepers that maintain the respective zones. In a distributed non-hierarchical gatekeeper architecture, there are no specified mechanisms for signaling between gatekeepers.
In addition, H.323 does not provide any caching management mechanisms for the information to be acquired dynamically between the gatekeepers. Moreover, there is no notion of gatekeeper-level routing so that messages can be sent between the gatekeeper for resolving the required information where multiple gatekeepers are involved. These signaling messages lack the required fields that will facilitate the notion of routing between the gatekeepers considering the multiple gatekeepers either in multiple zones of the giving domain and/or in multiple domains where a domain consists of one or more zones.